1. Field of the Invention
This invention relates to temperature-controlled road vehicles, and more especially to multicompartmented temperature-controlled road vehicles.
2. Description of the Prior Art
It has been well known for many years to provide an essentially closed delivery vehicle with an on-board refrigeration circuit.
Initially, only a single storage chamber was present, and air was cooled over the evaporator coils of the refrigeration unit, pumped into the chamber, recycled for further passage over the cooling coils of the evaporator, and so on. The heat absorbed by these coils was dissipated by passing the refrigerant fluid through an external condenser before recycling and expansion.
Subsequently, the need arose to provide the vehicle with two compartment for holding goods at different temperatures, e.g. frozen and chilled, or chilled and "controlled ambient" temperatures. This could be accommodated by generally maintaining the circuit of cold air as before in the colder compartment, but occasionally, e.g. as required by a thermostat, diverting a supply of such air to the less cold compartment. Alternative systems, e.g. involving a permanent bleed of colder air, were also possible.
More recently, three-compartment vehicles have been utilized. Various expedients have been adopted to ensure supplies of cool air, as needed, without cross-flavoring the compartment contents. Moreover, in recognition of the problem that there may be a warming requirement (e.g. because external temperature is below the "controlled ambient" requirement, or because of loss of heat through internal bulkheads to a deep-frozen compartment, with the same consequence), elaborate systems of sensing, and valving, and ducting, and reversal of evaporator action by passage of hot refrigerant, and application of extraneous heat supplies such as electrical fan heaters, have been proposed. In practice, with vehicles sold as suitable for operation in very hot or very cold climates, with different loadings of goods needing different conditions and with varying frequency of loading of compartments, the various temperature sensors in these vehicles can sometimes send conflicting operating signals to the compressor and to the valving of the ducted air supply, so that a prioritizing logic circuit is required for practical operation to deal with the compartments for optimum results.
There is nowadays a requirement for highly compartmented vehicles, e.g. six-compartment vehicles, and rapid changeover of storage conditions within each compartment. The present invention is based upon the realization that existing technology, based on sensor-controlled selective valving of supply ducting and ability to supply hot or cold air, is too complex to use in these multicompartment vehicles because of the possible interactions of the pressure and temperature conditions in the various compartments during the transient phases of operation.
Six-compartment vehicles are nowadays typically designed with six separate and thermally insulated longitudinal lanes of storage, three at a lower level and three at a higher level. The need for such vehicles does not exclusively reside in the ability to convey goods at six different temperatures, but has its origins in traffic congestion conditions at supermarkets or the like. Nowadays, to economize on stock and on holding space at their retail outlets (with high land values) it is typical for supermarkets to require frequent and smaller deliveries. Thus, a number of large specialist trucks will accumulate for unloading causing congestion, and must each moreover service say up to ten deliveries a day. Multicompartment and multi-temperature trucks, however, can each carry a range of delivery items, and consequently lead to less congestion and fewer deliveries each per day.
Such trucks, with elongate lanes, typically have movable floors which convey goods sequentially to the open rearward ends of the lanes and have also a relatively elaborate goods-handling loading/unloading mechanism which can operate between the floors, lower lane level and upper lane level in any one of three lane positions. Because they are used to convey a multi-product load they are typically loaded to a pre-existing program given to the driver for operation (or even fed in to the equipment at the depot) thus minimizing delivery error, theft or pressures on the driver for a larger or smaller delivery. Their complexity makes them an expensive prime cost, even though a fleet of such vehicles can be more cheaply operated, so that they are most economic if manufactured to the limit of legal sizes and weights.